1. Field of the Invention
This invention relates to odorizing systems for odorizing combustible gases and, more particularly, to a system including means for continuously monitoring the rate of odorant introduction into a pipeline that carries a combustible gas.
2. Description of the Prior Art
Natural gas is widely utilized in residential and industrial heating applications because it is a clean and efficient fuel for heating purposes. The gas is a mixture of light hydrocarbon gases which are found in the earth's crust, principally methane. In its natural form it is colorless and odorless, and therefore an odorizing agent is added to the gas in an amount sufficient to permit detection of the gas by smell and thereby identify when unintended flow or leakage of the gas is taking place.
The odorant materials most frequently used are mercaptans, which are organic compounds that contain sulphur and have a disagreeable odor that is easily detectable, even in extremely small amounts in the parts per billion range.
Natural gas pipeline systems have heretofore included means for periodic injection into the gas stream of a liquid odorant and the mixing of the odorant and gas as they travel through a pipeline in an effort to maintain a relatively constant odorant to gas ratio over the entire range of gas flow rates. The range of gas flow rates can vary widely, up to about 20:1, depending upon the season of the year and the user demand. Because the odor given off by the odorant is relatively strong, the presence of the odorant is easily detected and, therefore, only a very small quantity of odorant is needed to provide the necessary odorization. As a result, the amount of odorant required to be injected into a gas stream is in many instances far below the operating range of available liquid flow-meters. Typical odorant injection quantities range from about one-half to one and one-half pounds of odorant per million cubic feet of gas.
In the past, reliance has been placed upon the effective operation of the injection apparatus, and it has been assumed that the odorant was being injected as necessary and in the desired amount. However, because the odorizing equipment is normally installed at a location adjacent to the gas pipeline to be odorized, at a compressor station, or the like, and because that location is usually remote and unattended, any failure or malfunction of the odorizing equipment might not be detected and could result in the gas being inadequately odorized until the failure or malfunction is discovered and then corrected. In the meantime, inadequately odorized gas could be conveyed and any leakage or unintended flow could go undetected. Because of the safety hazard involved in the leakage of a combustible gas such as natural gas, which is explosive when mixed with air, some means for continuously monitoring the performance of the odorizer system is desirable in order to permit a rapid determination of any malfunction of the odorant addition operation. Additionally, it is desirable to provide a means to record the performance of gas odorizer systems, in terms of the amount of odorant actually added to the gas stream, in order to be able to demonstrate the proper operation of the odorant addition operation when called upon to do so.